|Basic info||Taxonomic history||Classification||Relationships|
|Morphology||Ecology and taphonomy||External Literature Search||Age range and collections|
Rhynchonellata - Orthida - Nanorthidae
If no rank is listed, the taxon is considered an unranked clade in modern classifications. Ranks may be repeated or presented in the wrong order because authors working on different parts of the classification may disagree about how to rank taxa.
|J. L. Benedetto and D. F. Muñoz 2017||Shell ventribiconvex to subequally biconvex. Ornamentation variably fascicostellate or parvicostellate; ribs rounded in profile, increasing mainly by lateral branching and, to a lesser extent, by interpolation, forming well-defined bundles distally. Medial portion of ventral valve usually accentuated by a stronger costella, which corresponds to a dorsal interspace. Ventral muscle field subtriangular or suboval in outline, with adductor field longer, wider and more elevated than diductors, bounded posteriorly by thick receding dental plates. Pedicle callist present. Notothyrial platform low, continuous with a broad, rounded median ridge not extending beyond the muscle field. Cardinal process absent or ridge-like. Fulcral plates visible at early ontogenetic stage, becoming progressively masked by secondary deposits with growth. Brachiophore plates varying through ontogeny from blade-like, subparallel, delimiting a small subrectangular notothyrial chamber, to partially or completely obliterated by secondary deposits. Dorsal muscle field quadripartite, deeply impressed; posterior adductor pair digitate or striated, of equal size or slightly larger than variably bilobed anterior adductor scars. Ventral vascular system saccate with ventral vascula media diverging laterally from their proximal extremities; dorsal vascular system apparently digitate.|